Organic Light Emitting Element and Display Device Using the Element

ABSTRACT

A hole transporting region made of a hole transporting material, an electron transporting region made of an electron transporting material, and a mixed region (light emitting region) in which both the hole transporting material and the electron transporting material are mixed and which is doped with a triplet light emitting material for red color are provided in an organic compound film, whereby interfaces between respective layers which exist in a conventional lamination structure are eliminated, and respective functions of hole transportation, electron transportation, and light emission are exhibited. In accordance with the above-mentioned method, the organic light emitting element for red color can be obtained in which power consumption is low and a life thereof is long. Thus, the display device and the electric device are manufactured by using the organic light emitting element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/444,889, filed Apr. 12, 2012, now allowed, which is a is acontinuation of U.S. application Ser. No. 12/978,678, filed Dec. 27,2010, now U.S. Pat. No. 8,174,007, which is a continuation of U.S.application Ser. No. 12/325,790, filed Dec. 1, 2008, now U.S. Pat. No.7,858,977, which is a continuation of U.S. application Ser. No.11/564,971, filed Nov. 30, 2006, now U.S. Pat. No. 7,459,722, which is adivisional of U.S. application Ser. No. 10/060,427, filed Jan. 29, 2002,now U.S. Pat. No. 7,173,370, which claims the benefit of a foreignpriority application filed in Japan as Serial No. 2001-025971 on Feb. 1,2001, all of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic light emitting element whichhas an anode, a cathode and a film comprising an organic compound inwhich light emission is obtained by applying an electric field(hereinafter referred to as organic compound film), and to a displaydevice using the organic light emitting element. The present inventionparticularly relates to a display device including organic lightemitting elements for emitting light of respective colors of red, greenand blue as pixels, in which emission efficiency of the element foremitting red color light is high and also, the element life is long.Note that the display device in this specification indicates an imagedisplay device using an organic light emitting element as a lightemitting element. Further, a module in which an organic light emittingelement is attached to a connector, for example, an anisotropicconductive film (FPC: flexible printed circuit), a TAB (tape automatedbonding) tape or a TCP (tape carrier package), a module in which aprinted wiring board is provided at an end of the TAB tape or TCP, and amodule in which an organic light emitting element is directly mountedwith an IC (integrated circuit) by a COG (chip on glass) method, all areincluded in the display devices.

2. Description of the Related Art

An organic light emitting element is an element that emits light byapplying an electric field. The light emission mechanism is described asfollows. A voltage is applied to electrodes sandwiching an organiccompound film, whereby an electron injected from a cathode and a holeinjected from an anode recombine in the organic compound film to form amolecule in an excitation state (molecular exciton). Then, the molecularexciton releases energy in returning to a base state, to emit light.

In such an organic light emitting element, in general, the organiccompound film is formed as a thin film with a thickness of less than 1μm. Further, the organic light emitting element is a self light emittingelement in which the organic compound film itself emits light, and thusdoes not need a backlight that is used in a conventional liquid crystaldisplay. Therefore, it is a great advantage that the organic lightemitting element can be extremely made thin and lightweight.

Further, for example, in the organic compound film with a thickness ofapproximately 100 to 200 nm, the time from carrier injection to carrierrecombination is approximately several tens of nanoseconds with takinginto consideration the carrier mobility of the organic compound film.Light emission is reached within microsecond even if the process fromcarrier recombination through light emission is considered. Therefore,it is one of strong points that a response speed is very high.

Furthermore, the organic light emitting element is a carrier injectiontype light emitting element. Thus, driving with a direct voltage ispossible, and noise is hard to be occurred. As regards a drivingvoltage, there is the following report; first, the organic compound filmis formed to be uniform and very thin with a thickness of approximately100 nm; further, an electrode material which makes small a carrierinjection barrier to the organic compound film, is selected; inaddition, a hetero structure (here, two-layer structure) is introduced;thus a sufficient bright ness of 100 cd/m² is realized at 5.5 V.(Reference 1: C. W. Tang and S. A. VanSlyke, “Organic electroluminescentdiodes,” Applied Physics Letters, vol. 51, No. 12, 913-915 (1987))

Besides the above-described element characteristics such as thinness andlightness, high-speed respondence and direct low voltage drive, it isone of great advantages that the organic light emitting element has alarge variety of emission colors. A factor for this advantage is thevariety of the organic compound itself. That is, the flexibilitv thatmaterials for various emission colors can be developed by moleculedesign (for example, introduction of a substituent) and the like leadsto richness in colors.

The most applied field of the organic light emitting element whichutilizes the richness in colors can be said to be a full-color flatpanel display. The reason for this is that, full color can be easilyattained by patterning the organic materials since there are a largenumber of organic materials capable of emitting the three primary colorsof light of red, green and blue. The element characteristics such asthinness and lightness, high-speed respondence and direct low voltagedrive as described above can be regarded as the characteristics suitablefor the flat panel display.

By the way, white color can be obtained by emitting light of all therespective colors of red, green and blue. The balance of the threeprimary colors of light needs to be considered in emitting white colorlight. Thus, minimum required efficiency (here, power efficiency, theunit is lm/W) with respect to each color is shown (Reference 2:Yoshiharu Sato, “Applied Physics Society OrganicMolecules—Bio-electronics Section,” Vol. 11. No. 1. P. 88 (2000)).

According to Reference 2, it is seen that there are a large number ofreports in which a required value is exceeded as to green color and bluecolor while a value for red color falls far short of a required value.Therefore, the improvement in emission efficiency of red color is anessential element for developing of the full-color flat panel display.Then, the improvement in the emission efficiency enables reduction inpower consumption.

It is given that a fluorescent material are used not only for a lightemitting material for red color but also for a general organic lightemitting element as one of factors in low emission efficiency. In theorganic light emitting element, light emission is occurred when amolecular exciton returns to a ground state. The light emission from asinglet excitation state (S*) (fluorescence) and the light emission froma triplet excitation state (T*) (phosphorescence) are possible as thelight emission. Only the light emission from S* (fluorescence) makes acontribution in the case where the fluorescent material is used.

However, a statistical generation ratio of S* to T* in the organic lightemitting element is considered to be S*:T*=1:3 (Reference 3: TetsuoTsutsui, “Applied Physics Society Organic Molecules—Bio-electronicsSection—Text of the Third Lecture Meeting.” P. 31 (1993)). Therefore,the theoretical limit of internal quantum efficiency (ratio of generatedphotons to injected carriers) in the organic light emitting elementusing the fluorescent material is established as 25% on the basis ofS*:T*=1:3. In other words, in case of the organic light emitting elementusing the fluorescent material, at least 75% of injected carriers arewasted.

On the contrary, it is considered that the emission efficiency isimproved (simply, three to four times) if the light emission from T*,that is, phosphorescence can be utilized. However, in a general organiccompound, the light emission from T* (phosphorescence) is not observedat a room temperature, and only the light emission from S*(fluorescence) is generally observed. The reason for this is that, sincethe base state of the organic compound is generally a singlet groundstate (S_(o)), T*−S_(o) transition is forbidden transition whileS*−S_(o) transition is allowed transition.

However, the presentations on an organic light emitting element capableof converting energy released in returning to a ground state from T*(hereinafter referred to as “triplet excitation energy”) into lightemission have been given one after another in recent years, and thehighness of the emission efficiency has attracted attention. (Reference4: D. F. O'Brien, M. A. Baldo, M. E. Thompson and S. R. Forrest.“Improved energy transfer in electrophosphorescent devices.” AppliedPhysics Letters, vol. 74, No. 3, 442-444 (1999)). (Reference 5: TetsuoTsutsui. Moon-Jae Yang, Masayuki Yahiro, Kenji Nakamura, TeruichiWatanabe, Taishi Tsuji, Yoshinori Fukuda, Takeo Wakimoto and SatoshiMiyaguchi. “High Quantum Efficiency in Organic Light-Emitting Deviceswith Iridium-Complex as a Triplet Emissive Center,” Japanese Journal ofApplied Physics, Vol. 38. L1502-L1504 (1999))

A metal complex with platinum as central metal (hereinafter referred toas “platinum complex”) and a metal complex with iridium as central metal(hereinafter referred to as “iridium complex”) are used as lightemitting materials in Reference 4 and Reference 5, respectively. It canbe said that these metal complexes have such a feature that a thirdtransition series element is introduced as the central metals. Both ofthe complexes are materials capable of converting triplet excitationinto light emission at a room temperature (hereinafter referred to as“triplet light emitting material”).

As shown in Reference 4 and Reference 5, an organic light emittingelement capable of converting triplet excitation energy into lightemission can attain a higher internal quantum efficiency in comparisonwith prior art. Then, as the internal quantum efficiency becomes higher,the emission efficiency (lm/W) is improved. Therefore, if the lightemitting element for red color is manufactured by using the organiclight emitting element capable of converting triplet excitation energyinto light emission (hereinafter referred to as “triplet light emittingelement”), the emission efficiency of the red color light emittingelement can be improved.

From the above, an organic light emitting element that presents thelight emission from a singlet excitation state (hereinafter referred toas “singlet light emitting element”) is used for green color and bluecolor while the triplet light emitting element is applied for red color,whereby the full-color flat panel display with sufficiently highbrightness and low power consumption, in which the balance of the threeprimary colors of light is considered, is expected to be manufactured.

However, according to the report of Reference 5, the half-life of thebrightness in constant current drive is approximately 170 hours when theinitial brightness is set to 500 cd/m², and thus, the triplet lightemitting element has a problem on an element life. On the other hand, incase of the singlet light emitting element, the half-life of thebrightness at constant current drive is several thousands of hours toten thousands hours when the initial brightness is set at 500 cd/m².Thus, it can be said that the singlet light emitting element reaches thepractical stage in terms of an element life.

Therefore, in prior art, when the singlet light emitting element is usedfor green color and blue color while the triplet light emitting elementis applied for red color to thereby manufacture the full-color flatpanel display, a change of brightness in time largely differs between apixel for green color or blue color and a pixel for red color.

Namely, this indicates that the balance of the three primary colors oflight is greatly lost with the lapse of time (after several hundred ofhours), and along with this, the power consumption in of light emissionof red color increases. Therefore, it can be said that an extremelyimportant technical object is to lengthen the life of the triplet lightemitting element, particularly, the life of the triplet light emittingelement for red color.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and an objectof the present invention is therefore to suppress reduction inbrightness of a triplet light emitting element for red color and tolengthen a life of the element, and another object of the presentinvention is to provide an organic light emitting element for red colorwith higher light emission efficiency and a longer life.

Further, still another object of the present invention is to provide adisplay device, in which a balance of three primary colors of light ismore favorable, besides, power consumption is lower, and a change offluctuation among colors with time is smaller than prior art, by usingthe triplet light emitting element for red color and singlet lightemitting elements for green color and blue color. Furthermore, yet stillanother object of the present invention is to provide an electric devicewith lower power consumption than prior art and a display portionexhibiting a clear display that never fades even with the lapse of time,by using the display device.

Regardless of the difference between the singlet light emitting elementand the triplet light emitting element, an organic light emittingelement generally has a characteristic that a lamination structure(hetero structure) as shown in Reference 1, is formed. In Reference 1,for example, a single hetero structure, in which a hole transportinglayer composed of an aromatic diamine compound and an electrontransporting light emitting layer composed oftris(8-quinolinolate)-aluminum (hereinafter referred to as “Alq₃”) arelaminated, is applied to an organic compound film, whereby carrierrecombination efficiency is enhanced steeply. This is described asfollows.

For example, in case of the organic light emitting element onlyincluding an Alq₃ single layer, most of electrons injected from acathode do not recombine with holes and reach an anode since Alq₃ haselectron transporting property. Thus, the emission efficiency isextremely low. That is, it is necessary to use a material capable oftransporting both of the electrons and the holes with keeping stablebalance (hereinafter referred to as “bipolar material”) in order to makethe organic light emitting element with a single layer emit light withefficiency (or to drive at a low voltage). Alq₃ does not meet therequirement.

However, when the single hetero structure shown in Reference 1 isapplied, the electrons injected from the cathode are blocked at aninterface of the hole transporting layer and the electron transportinglight emitting layer, and are sealed in the electron transporting lightemitting layer. Therefore, carrier recombination is performed in theelectron transporting light emitting layer with efficiency to lead tolight emission with efficiency. That is, a blocking function of thecarrier due to the introduction of the hetero structure is the core of atechnique.

Further, in the organic light emitting element in Reference 1,separation of functions is realized, that is, the hole transportinglayer conducts transportation of holes and the electron transportinglight emitting layer conducts transportation of electrons and lightemission. The advantage of such function separation is that one kind oforganic material does not need to simultaneously have various functions(light emitting property, carrier transporting property, carrierinjecting property from an electrode, and the like) by realizing thefunction separation, and thus, molecule design and the like can have awide degree of freedom (For example, it is not necessary to forcedlylook for the bipolar material). That is, a material with a satisfactorylight emitting characteristic, a material with an excellent carriertransporting property and the like are combined one another, wherebyhigh emission efficiency can be easily achieved.

However, the lamination structure as described above is the junction ofdifferent substances. Thus, an interface (hereinafter referred to as“organic interface”) is occurred between respective layers. Theinfluence on the life of the organic light emitting element isconsidered as the problem that derives from the formation of the organicinterface. That is, the carrier movement is disturbed at the organicinterface, and the brightness is lowered due to accumulation of charge.

Although no definite theory has been established regarding the mechanismof this degradation, it has been reported that the reduction inbrightness can be suppressed by inserting a hole injecting layer betweenthe anode and the hole transporting layer, and in addition, byperforming ac drive at a rectangular wave instead of dc drive (Reference5: S. A. VanSlyke, C. H. Chen, and C. W. Tang. “Organicelectroluminescent devices with improved stability.” Applied PhysicsLetters, Vol. 69, No. 15, 21-2162 (1996)). This can be said to beexperimental evidence that the reduction in brightness can be suppressedin accordance with eliminating charge accumulation by adding the holeinjecting layer and by using the ac drive.

Here, the element structure of the triplet light emitting element forred color shown in Reference 4 is shown in FIG. 1. In FIG. 1,4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereinafter referredto as “α-NPD”) is used for a hole transporting layer,4,4′-dicarbazole-biphenyl (hereinafter referred to as “CBP”) is used asa host material of a light emitting layer,2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin-platinum (hereinafterreferred to as “PtOEP”) is used for a triplet light emitting material,basocuproin (hereinafter referred to as “BCP”) is used for a blockinglayer. Alq₃ is used for an electron transporting layer, and Mg:Ag alloyis used for a cathode.

The triplet light emitting element generally needs the host materialappropriate for the light emitting material (in FIG. 1, CBP) and ablocking material for preventing diffusion of molecular excitons (inFIG. 1, BCP), and thus, takes the multilayer structure as shown inFIG. 1. Thus, a large number of organic interfaces are generated.Therefore, it is considered that this is a factor for the short life ofthe triplet light emitting element.

In order to overcome the above problem, it is important to consider thereason that the carrier movement is disturbed at the organic interfaceand to improve it. Then, the present inventor first thought of twomechanisms described below as models in which the carrier movement isdisturbed due to the formation of the organic interface.

First, as one of the mechanisms, a mechanism that derives frommorphology of the organic interface may be given. The organic compoundfilm in the organic light emitting element is generally a film in anamorphous state, and is formed by cohering molecules of the organiccompound with each other with a force among the molecules mainlycomposed of dipole interaction. However, if the hetero structure isformed by using an aggregate of the molecules, there is a possibilitythat the difference among the molecules in size and shape greatlyinfluences the interface of the hetero structure (that is, the organicinterface).

In particular, in the case forming the hetero structure by usingmaterials in which molecules greatly differ one another in size, it isconsidered that the conformity of the junction in the organic interfaceis deteriorated. The conceptual diagram is shown in FIG. 2. In FIG. 2, afirst layer 211 consisting of small molecules 201 and a second layer 212consisting of large molecules 202 are laminated. In this case, regions214 with poor conformity are occurred at a formed organic interface 213.

The regions 214 with poor conformity shown in FIG. 2 may become barrierswhich disturb the carrier movement (or energy barriers), and thus, it issuggested that the regions 214 become an obstacle for further reductionin a driving voltage. Further, there is a possibility that the carrierthat cannot go over the energy barrier is accumulated as charge, whichinvites the reduction in brightness as described above.

As another mechanism, a mechanism that derives from the process offorming the lamination structure (that is, forming the organicinterface) can be given. The organic light emitting element with thelamination structure is generally manufactured by using a multi-chambertype (in-line type) evaporation apparatus shown in FIG. 3 in order toavoid contamination in the formation of the respective layers from theviewpoint of blocking of the carrier and function separation.

FIG. 3 is a conceptual diagram of an evaporation apparatus for forming athree-layer structure (double hetero structure) of a hole transportinglayer, a light emitting layer and an electron transporting layer. First,a substrate having an anode (indium-tin oxide (hereinafter referred toas “ITO”) or the like) is carried into a loading chamber, and then, isirradiated with ultraviolet rays in a vacuum atmosphere in anultraviolet ray irradiation chamber, whereby the surface of the anode iscleaned. Particularly in the case where the anode is oxide such as ITO,an oxidization process is performed in a pretreatment chamber. Further,in order to form the respective layers of the lamination structure, thehole transporting layer is formed in an evaporation chamber 301, thelight emitting layers are formed in evaporation chambers 302 to 304 (inFIG. 3, three colors of red, green and blue), the electron transportinglayer is formed in an evaporation chamber 305, and a cathode is formedby evaporation in an evaporation chamber 306. Finally, sealing isconducted in a sealing chamber, and then, the substrate is carried outfrom an unloading chamber. Thus, an organic light emitting element isobtained.

The characteristic of such an in-line type evaporation device is thatthe respective layers are formed by evaporation in the differentevaporation chambers 301 to 305. That is, the device has a structurethat materials for the respective layers are hardly mixed with eachother.

By the way, although the inside of the evaporation device is generallydecompressed to approximately 10⁻⁴ to 10⁻⁵ pascal, a very small amountof gas components (oxygen, moisture and the like) exists. Then, in caseof the degree of vacuum as described above, it is said that even thevery small amount of gas components easily forms an absorption layer ofapproximately a monolayer only in several seconds.

In the case of manufacturing the organic light emitting element with thelamination structure by using the device in FIG. 3, it is a problem thata large interval is generated between the formation of the respectivelayers. That is, there is a fear that the absorption layer composed ofthe very small amount of gas components (hereinafter referred to as“impurity layer”) is formed in the interval between the formation of therespective layers, particularly in transferring the substrate through asecond transfer chamber.

The impurity layer formed between the respective layers (that is, on theorganic interface) becomes an impurity region that traps the carrier tointerfere with the carrier movement after the completion of the organiclight emitting element. Thus, the impurity layer also causes a drivingvoltage to rise. Further, when the impurity region that traps thecarrier exists, charge is accumulated in the region. Thus, there is apossibility that the above-described reduction in brightness is invited.

Taking the above-described mechanisms into consideration, it is requiredthat the conventional lamination structure element is superseded by newone in terms of both an element structure and a manufacturing process inorder to overcome the problem on the organic interface (deterioration ofmorphology of the organic interface and formation of the impuritylayer).

In addition, in case of the triplet light emitting element, there is alimitation that function separation should be realized as the case ofthe lamination structure element. The reason for this is that a lightemitting region in which doping is conducted to a proper host materialneeds to be provided since the triplet light emitting material has poorcarrier transporting property and has to be used as dopant. Further,since a diffusion length of a triplet molecular exciton is longer thanthat of a singlet molecular exciton, a blocking material for preventingdiffusion of the molecular excitons is also required. That is, even ifthe organic interface is removed, the triplet light emitting elementdoes not reach the light emission with efficiency without the functionseparation of the organic compound film.

Taking the above into consideration, the present inventor devised atechnique for realizing a triplet light emitting element in which anorganic interface is removed and function separation is realized in anorganic compound film. The conceptual diagrams are shown in FIGS. 4A and4B and FIG. 5.

In FIG. 4A, in an organic compound film 403, a hole transporting region405 composed of a hole transporting material, an electron transportingregion 406 composed of an electron transporting material and a mixedregion 407 in which the hole transporting material and the electrontransporting material are mixed are provided. Further, a triplet lightemitting material 408 is doped in the mixed region 407. Here, althoughan anode 402 is provided on a substrate 401, the inverse structure maybe taken in which a cathode 404 may be provided on the substrate.

In the case of forming such an element, the hole transporting materialcan receive and transport holes at the anode side while the electrontransporting material can receive and transport electrons at the cathodeside. Further, since the mixed region 407 has bipolar property, both theholes and the electrons can move in the mixed region 407. Thus, carriersrecombine in the mixed region 407 leads to light emission. However, inthis case, it is preferable that the energy difference between a highestoccupied molecular orbital (HOMO) and a lowest unoccupied molecularorbital (LUMO) (hereinafter referred to as “excitation energy level”) ofthe triplet light emitting material is small in comparison with the holetransporting material and the electron transporting material from theviewpoint that the diffusion of the triplet molecular excitons isprevented.

Further, in the element shown in FIG. 4A, the regions in whichrespective functions can be expressed exist in the organic compound film403. The expression of the functions is realized, and besides, theorganic interface which is seen in the conventional lamination structuredoes not exist. Therefore, the problem that derives from theabove-described organic interface (deterioration of the morphology ofthe organic interface and formation of the impurity layer) can besolved.

First, the solution for the deterioration of the morphology of theorganic interface will be explained with reference to FIG. 6. FIG. 6shows an organic light emitting element disclosed in the presentinvention, which is constituted of a region 611 consisting smallmolecules 601, a region 612 consisting of large molecules 602 and amixed region 613 including both the small molecules 601 and the largemolecules 602. As apparent from FIG. 6, the organic interface. 213 whichexists in FIG. 2, does not exist, and the region 214 with poorconformity does not exist, either.

Further, the solution for the formation of the impurity layer is simpleand clear. In the case of forming the organic light emitting element inFIGS. 4A and 4B, it is favorable to conduct the process as follows. Thehole transporting material is evaporated on the anode, the electrontransporting material is started to evaporate thereon on the midway inthe form of co-evaporation to form the mixed region, the evaporation ofthe hole transporting material is stopped after the formation of themixed region, and then, the electron transporting material isevaporated. Therefore, the interval as shown in FIG. 2 does not exist,which is generated when the organic light emitting element ismanufactured by using the evaporation device. That is, the time forforming the impurity layer does not exist.

As described above, in the triplet light emitting element of the presentinvention, the carrier movement is smooth since the organic interface isnot formed. Thus, the element life is not adversely affected. Further,the function separation is realized as in the lamination structure, andthus, there is no problem on emission efficiency, either.

Note that, in FIG. 4A, a hole injecting region composed of a materialfor enhancing hole injecting property (hereinafter referred to as “holeinjecting material”) may be inserted between the anode and the organiccompound film. Further, an electron injecting region composed of amaterial for enhancing electron injecting property (hereinafter referredto as “electron injecting material”) may be inserted between the cathodeand the organic compound film. Furthermore, both the hole injectingregion and the electron injecting region may be inserted.

In this case, the hole injecting material or the electron injectingmaterial is a material for making small the barrier for carrierinjection from the electrode to the organic compound film, and thus hasan effect that the carrier movement from the electrode to the organiccompound film is smoothened and the accumulation of charge is removed.However, it is preferable that the respective injecting materials andthe organic compound film are deposited without putting an intervaltherebetween from the viewpoint as described above that the formation ofthe impurity layer is avoided.

Further, the light emitting region is kept distant from both theelectrodes as much as possible, whereby quenching due to the energymovement to the electrode material can be prevented. Therefore, in theorganic light emitting element as shown in FIG. 4A, the region to whichthe triplet light emitting material is doped may not be the entireregion of the mixed region 407 but a part of the region (especially, thecenter portion).

Furthermore, as shown in FIG. 4B, it is preferable that, besides thetriplet light emitting material 408, a blocking material 409 is doped tothe mixed region 407. The blocking material 409 is a material with afunction of blocking a carrier or a molecular exciton, and preferablyhas the largest excitation energy level among the materials contained inthe mixed region 407. The doping of the blocking material enables theimprovement in a carrier recombination rate in the mixed region 407 andthe prevention of the diffusion of the molecular excitons. Thus, it isconsidered that the emission efficiency is improved.

Note that the blocking material 409 may be doped over the mixed region407. However, the blocking material generally has a function of blockingone of a hole and an electron in many cases, and thus, the carrierbalance in the mixed region may be lost if the doping is conducted tothe entire mixed region. Therefore, the region to which the blockingmaterial is doped may not be the entire mixed region but a part of theregion (especially, the end portion).

In particular, in the case where the blocking material 409 has holeblocking property, the hole blocking material is doped to the areacloser to the cathode side than the region to which the triplet lightemitting material 408 is doped as shown in FIG. 4B, whereby lightemission is obtained with efficiency.

By the way, it is preferable that a concentration gradient is formed inthe mixed region containing both the hole transporting material and theelectron transporting material, so that the concentration of the holetransporting material gradually decreases while the concentration of theelectron transporting material gradually increases in the direction fromthe anode toward the cathode from the viewpoint of control of thecarrier balance. Further, in the present invention, the mixed region isalso a carrier recombination region. Thus, it is desirable that themixed region has a thickness of 10 nm or more.

By the way, the organic interface is removed, and besides, the functionsare exhibited with the element structure in which the triplet lightemitting material is doped into the mixed region composed of the holetransporting material and the electron transporting material so far. Inaddition, it is an effective means that the mixed region is provided inthe organic interface in the lamination structure on the basis of theconventional lamination structure in FIG. 1. The conceptual diagram isshown in FIG. 5.

FIG. 5 shows an organic light emitting element, in which an anode 502, ahole injecting region 503 composed of a hole injecting material, a holetransporting region 504 composed of a hole transporting material, alight emitting region 505 including a host material to which a tripletlight emitting material is doped, a blocking region 506 composed of ablocking material, an electron transporting region 507 composed of anelectron transporting material, an electron injecting region 508composed of an electron injecting material and a cathode 509, areprovided on a substrate 501. All the regions 503 to 508 do not need tobe used in the present invention, and it is sufficient that at least theregions 504 to 507 exist. However, all the regions are shown for thesake of convenience. Note that the anode 502 is provided on thesubstrate 501 here, but the inverse structure may be taken in which thecathode 509 is provided on the substrate.

At this time, a characteristic of the present invention is thatrespective materials used for upper and lower regions in the spaceconcerned (for example, the hole transporting material and the hostmaterial in case of a space 512) are mixed in any one of spaces 511 to515 each between the respective regions. In other words, although thespaces 511 to 515 each between the respective regions are shown bybroken lines in FIG. 5, no organic interface actually exists. It can besaid that mixed regions are provided.

In the triplet light emitting element as well, the carrier movement issmooth since the organic interface is not formed. Thus, the element lifeis not adversely affected. Further, the function separation is realizedas in the lamination structure, and thus, there is no problem onemission efficiency, either.

As described above, while the conventional lamination structure is thesimple junction (hetero-junction) of different substances, thestructures of the present invention, which are exemplified in FIGS. 4Aand 4B and FIG. 5, are, as it were, mixed-junctions. Thus, it can besaid that the organic light emitting elements shown in FIGS. 4A and 4Band FIG. 5 are organic light emitting elements based on the new concept.

Further, the triplet light emitting material for red color is used forthe triplet light emitting element based on the concept shown in FIGS.4A and 4B and FIG. 5, whereby an organic light emitting element for redcolor can be provided in which emission efficiency is higher and a lifeis longer than prior art. Further, a display device can be manufacturedin which a balance of the three primary colors of light is morefavorable, besides, power consumption is lower, and a change of colorfluctuation with time is smaller than prior art, by using the tripletlight emitting element for red color and singlet light emitting elementsfor green color and blue color.

Furthermore, in the above-described display device, it is preferablethat the mixed junction as disclosed in the present invention isimplemented in the singlet light emitting elements for green color andblue color, not the conventional lamination structure. That is, it isfavorable that the triplet light emitting material to be doped issubstituted with the singlet light emitting material for green color orblue color, or that a carrier transporting material is made to emitlight without doping (or a material for emitting light of green color orblue color is selected) in FIGS. 4A and 4B or FIG. 5.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows a structure of a conventional organic light emittingelement;

FIG. 2 shows a state of an organic compound film;

FIG. 3 shows a structure of an evaporation device;

FIGS. 4A and 4B show structures of an organic light emitting element;

FIG. 5 shows a structure of an organic light emitting element;

FIG. 6 shows a state of an organic compound film;

FIGS. 7A and 7B show structures of an evaporation device;

FIG. 8 shows a structure of an evaporation device;

FIGS. 9A to 9E show a procedure of forming a display device;

FIGS. 10A to 10C show structures of respective pixels;

FIG. 11 shows a cross sectional structure of a display device;

FIG. 12 shows a cross sectional structure of a display device;

FIG. 13 shows a cross sectional structure of a display device;

FIGS. 14A and 14B show a top surface structure and a cross sectionalstructure of a display device;

FIGS. 15A to 15C show a top surface structure and cross sectionalstructures of a display device;

FIGS. 16A and 16B show structures of a display device;

FIGS. 17A and 17B show structures of a display device;

FIGS. 18A to 18C show structures of a display device;

FIGS. 19A to 19F show specific examples of electric devices; and

FIGS. 20A and 20B show specific examples of electric devices.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment mode in implementing the present inventionwill be described. Note that, in an organic light emitting element, itis sufficient that at least one of an anode and a cathode is transparentin order to obtain light emission. In the present embodiment mode,description is made on the basis of an element structure in which atransparent anode is formed on a substrate to take out light from theanode. In actuality, it is also possible to apply the present inventionto a structure in which a transparent cathode is formed on a substrateto take out light from the cathode and a structure in which light istaken out from the opposite side to a substrate.

In implementing the present invention, a manufacturing process of theorganic light emitting element is important in order to prevent theformation of an impurity layer. Then, first, a method of manufacturing atriplet light emitting element having a, mixed region, which isdisclosed in the present invention, is described while focused on theformation of the mixed region.

FIG. 7A is a top view of an evaporation device. The evaporation deviceis of a single chamber type in which one vacuum tank 710 is arranged asan evaporation chamber, and a plurality of evaporation sources areprovided in the vacuum tank. Then, various materials having differentfunctions such as a hole injecting material, a hole transportingmaterial, an electron transporting material, an electron injectingmaterial, a blocking material, a light emitting material, and aconstituent material for a cathode are separately provided in theplurality of evaporation sources, respectively.

In the evaporation device having the evaporation chamber as describedabove, first, a substrate having an anode (ITO or the like) is carriedinto a loading chamber. In the case where the anode is oxide such asITO, an oxidization process is conducted in a pretreatment chamber (Notethat, although not shown in FIG. 7A, it is also possible to provide anultraviolet ray irradiation chamber in order to clean the surface of theanode). Further, all the materials for forming the organic lightemitting element are evaporated in the vacuum tank 710. However, acathode may be formed in the vacuum tank 710, or another evaporationchamber may be provided to form the cathode therein. In short, it isfavorable that evaporation is conducted in the vacuum tank 710 upthrough the formation of the cathode. Finally, sealing is conducted in asealing chamber, and the substrate is carried out from an unloadingchamber to obtain an organic light emitting element.

The procedure of manufacturing the triplet light emitting elementaccording to the present invention using such a single chamber typeevaporation device is described with reference to FIG. 7B (crosssectional view of the vacuum tank 710). FIG. 7B shows a process offorming an organic compound film constituted of a hole transportingmaterial 721, in electron transporting material 722, and a triplet lightemitting material 723 by using the vacuum tank 710 which has the threeevaporation sources (an organic compound evaporation source a 716, anorganic compound evaporation source b 717, and an organic compoundevaporation source c 718) as the most simple example.

First, a substrate 701 having an anode 702 is carried into the vacuumtank 710, and is fixed by a fixing table 711 (the substrate is generallymade to rotate at the time of evaporation). Next, the inside of thevacuum tank 710 is decompressed (10⁻⁴ pascal or less is preferable), andthen, a container a 712 is heated to vaporize the hole transportingmaterial 721. After a predetermined evaporation rate (unit: Å/s) isobtained, a shutter a 714 is opened to thereby start evaporation. Atthis time, a container b 713 is also heated with shutter b 715 closed.

Thereafter, the shutter b 715 is opened with the shutter a 714 opened,and thus the electron transporting material 722 is co-evaporated to forma mixed region 704 after the formation of a hole transporting region703. Accordingly, an impurity layer is not mixed between the holetransporting region 703 and the mixed region 704. Note that a very smallamount of the triplet light emitting material 723 is also doped upon theformation of the mixed region 704 (the state shown in FIG. 7B).

Further, in order to form an electron transporting region, the shutter a714 is closed with the shutter b 715, and heating of the container a 712is finished. Accordingly, an impurity layer is not formed between themixed region 704 and the electron transporting region.

Note that, in the case where a hole injecting region or an electroninjecting region is formed, evaporation sources for respective injectingmaterials may be provided in the same vacuum tank 710. In FIG. 7B, forexample, in the case where the hole injecting region is provided betweenthe anode 702 and the hole transporting region 703, the holetransporting material 721 is vaporized without putting an interval afterthe hole injecting material is evaporated onto the anode 702. Thus, theformation of the impurity layer can be avoided.

If the above-described method is applied, it is possible to manufactureall the organic light emitting elements described in “summary of theinvention.” For example, even in the case where the mixed regions areprovided between the respective regions as shown in FIG. 5, it ispossible to utilize the similar co-evaporation. In this case as well,the formation of the impurity layer can be avoided since the intervaldoes not exist. Further, the organic light emitting elements can bemanufactured by a similar technique also in the case where the mixedregions are provided in a singlet light emitting element.

Next, an evaporation procedure for each pixel in manufacturing a displaydevice is shown in schematic diagrams of FIG. 8 and FIGS. 9A to 9E. FIG.8 shows an example of an evaporation device with which the displaydevice can be manufactured. The evaporation device seems similar to thatshown in FIG. 3 at first glance, but there is a greatly different pointbetween them. Differently from the evaporation device shown in FIG. 3 inwhich the separate evaporation chambers are provided for the respectivelayers (that is, respective materials) of the lamination structure,evaporation chambers are separately provided for the formation of pixelsof respective colors (red, green and blue) and evaporation sources ofall the materials (except for a cathode material) for forming a certaincolor pixel are provided in one evaporation chamber (801, 802 or 803) inthe evaporation device shown in FIG. 8.

What is important is that, as regards the certain color pixel concerned,all the functional materials (hole transporting material, electrontransporting material and the like) are evaporated without intervals upthrough the formation of the cathode to thereby prevent the formation ofthe impurity layer. Note that it is favorable that the cathode isfinally deposited in common with pixels in a cathode evaporation chamber804.

In this case, the impurity layer is formed between the cathode and theelectron transporting region (or electron injecting region). However,the cathode material is injected into the electron transporting region(or electron injecting region) to some extent as in sputtering when thecathode is evaporated. This effect enables the impurity layer to beremoved, and thus, a problem is not occurred. Of course, the depositionof the cathode may be conducted in each of the evaporation chambers (801to 803).

A shadow mask which is a known technique is used for the application ofrespective colors of pixels. The state thereof is shown in FIGS. 9A to9E. First, as shown in FIG. 9A, a substrate 901 on which a transparentelectrode (anode) 902, is divided into a red pixel 911, a green pixel912, and a blue pixel 913 by a bank-shaped structure 903, is carriedinto the evaporation chamber 801 for red pixel to form an organiccompound film 904 for red pixel (the hole injecting region or electroninjecting region may exist or not, but is omitted here.) At this time,the substrate is covered by a metal mask 914 patterned so that thematerial is not mixed into pixels of other colors (blue pixel and greenpixel) (FIG. 9B).

Next, the substrate is carried into the evaporation chamber 802 forgreen pixel to form an organic compound film 905 for green pixel. Themetal mask 914 is at the position shifted from the previous position, sothat the material is not mixed into other pixels (FIG. 9C). This issimilar to the case of the formation of an organic compound film 906 forblue pixel (FIG. 9D). Finally, in the cathode evaporation chamber 804, acathode 907 is deposited in common with the three pixels (FIG. 9E).

Note that the order of the formation of the organic compound films ofthe respective color pixels may be any order. In the above-mentionedmanufacturing method of the display device, the formation is conductedin the order of red, green and blue.

Preferred materials for a hole injecting material, a hole transportingmaterial, an electron transporting material, an electron injectingmaterial, a blocking material, a light emitting material, a constituentmaterial for a cathode, and the like are listed below. However, thematerials used for the organic light emitting element of the presentinvention are not limited thereto.

Porphyrin-based compounds are effective among organic compounds as thehole injecting materials, and phthalocyanine (hereinafter referred to as“H₂Pc”), capper phthalocyanine (hereinafter referred to as “CuPc”), andthe like are gi, en. There exist materials in which chemical doping isconducted to a conductive polymer compound, and polyethylenedioxythiophene (hereinafter referred to as “PEDOT”) doped withpolystyrenesulfonic acid (hereinafter referred to as “PSS”),polyaniline, polyvinyl carbazole (hereinafter referred to as “PVK”), andthe like can be given. Further, a polymer compound of insulator iseffective in terms of flatness of an anode, and polyimide (hereinafterreferred to as “PI”) is often used. In addition, an inorganic compoundis used, and an ultrathin film of aluminum oxide (hereinafter referredto as “alumina”) is given besides a metal thin film made of gold,platinum or the like.

Aromatic amine-based (that is, with bond of benzene ring and nitrogen)compounds are most widely used as the hole transporting materials. Asthe materials widely used, there can be given, in addition toabove-described TPD, starburst type aromatic amine-based compounds suchas 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereinafterreferred to as “α-NPD”) that is a derivative thereof,4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine (hereinafter referred toas “TDATA”), and4,4′,4″-tris[N-(3-methylphenol)-N-phenyl-amino]-triphenylamine(hereinafter referred to as “MTDATA”).

Metal complexes are often used as the electron transporting materials,and metal complexes having a quinoline skeleton or a benzoquinolineskeleton such as above-described Alq₃,tris(4-methyl-8-quinolinolate)aluminum (hereinafter referred to as“Almq₃”) and bis(10-hydroxybenzo[h]-quinolinate beryllium (hereinafterreferred to as “BeBq₂”),bis(2-methyl-8-quinolinolate)-(4-hydroxy-biphenyl)-aluminum (hereinafterreferred to as “BAlq₂”) that is a mixed ligand complex, and the like aregiven. Also, there are given metal complexes having oxazole or thiazoleligand such as bis[2-(2-hydroxyphenyl)-benzooxazolate]zinc (hereinafterreferred to as “Zn(BOX)₂”) andbis[2-(2-hydroxyphenyl)-benzothiozolate]zinc (hereinafter referred to as“Zn(BTZ)₂”). Furthermore, in addition to the metal complexes, oxadiazolederivatives such as2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (hereinafterreferred to as “PBD”) and1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene(hereinafter referred to as “OXD-7”), triazole derivatives such as3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenyl)-1,2,4-triazole(hereinafter referred to as “TAZ”) and3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenyl)-1,2,4-triazole(hereinafter referred to as “p-EtTAZ”), and phenanthroline derivativessuch as bathophenanthroline (hereinafter referred to as “BPhen”) andbathocuproin (hereinafter referred to as “BCP”) have electrontransporting property.

The above-described electron transporting materials can be used as theelectron injecting materials. In addition, an ulrtathin film, which isformed of insulator such as an alkali metal halide such as lithiumfluoride or alkali metal oxide such as lithium oxide, is often used.Further, alkali metal complexes such as lithium acetylacetonate(hereinafter referred to as “Li(acac)”) and 8-quinolinolate-lithium(hereinafter referred to as “Liq”) are also effective.

As the blocking materials. BAlq, OXD-7, TAZ, p-EtTAZ, BPhen, BCP, andthe like described above are effective because of the high excitationenergy level.

As the triplet light emitting materials for red color, there are known2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin-platinum (hereinafterreferred to as “PtOEP”),bis[2-(2-pyridyl)-benzo[b]thiophene]-acetylacetonate-iridium(hereinafter referred to as “Ir(btp)₂(acac)” and the like.

EMBODIMENTS Embodiment 1

In this embodiment, an organic light emitting element shown in FIG. 4A,in which an electron injecting region composed of an electron injectingmaterial is inserted between a cathode 404 and an organic compound film403, is specifically exemplified.

First, ITO is deposited into a film with a thickness of approximately100 nm by sputtering, and a glass substrate 401 on which an anode 402 isformed is prepared. The glass substrate 401 having the anode 402 iscarried into the vacuum tank as shown in FIGS. 7A and 7B. In thisembodiment, five evaporation sources are needed since five kinds ofmaterials (four kinds corresponding to organic compounds and one kindcorresponding to metal to be a cathode) are evaporated.

Then, α-NPD that is the hole transporting material is evaporated at anevaporation rate of 3 Å/s to form a hole transporting region with athickness of 40 nm. Thereafter, while the evaporation rate for α-NPD isfixed at 3 Å/s, evaporation of BAlq₂ that is the electron transportingmaterial is started also at an evaporation rate of 3 Å/s. That is, amixed region 407 in which the ratio of the rates of α-NPD and Alq₃ is1:1 is formed by co-evaporation.

The mixed region 407 is formed with a thickness of 30 nm, and at thistime, the middle region corresponding to 20 nm in the mixed region 407(that is, 5 nm to 25 nm in 30 nm of the mixed region) is doped withPtOEP that is the triplet light emitting material for red color as alight emitting material 408 at a rate of 4 wt %, α-NPD and BAlq₂ eachhave high excitation energy level, and thus, a blocking material 409 asshown in FIG. 4B is not required in case of this embodiment.

After the thickness of the mixed region 407 reaches 310 nm, while theevaporation of α-NPD is completed, the evaporation of BAlq, iscontinued, whereby an electron transporting region 406 is formed. Thethickness is set to 10 nm. Further, the evaporation of BAlq₂ iscompleted and at the same time, evaporation of Alq₃, which is theelectron injecting material, is started without putting an interval toevaporate by approximately 40 nm. The reason the interval is not put isthat the formation of an impurity layer is prevented as described above.Finally, an Al:Li alloy as the cathode is evaporated to have a thicknessof approximately 150 nm. Thus, a triplet light emitting element foremitting red color which derives from PtOEP is obtained.

Embodiment 2

In this embodiment, an organic light emitting element shown in FIG. 5 isspecifically exemplified.

First, ITO is deposited into a film with a thickness of approximately100 nm by sputtering, and a glass substrate 501 on which an anode 502 isformed is prepared. The glass substrate 501 having the anode 502 iscarried into a vacuum tank as shown in FIGS. 7A and 7B. In thisembodiment, eight evaporation sources are needed since eight kinds ofmaterials (seven kinds corresponding to organic compounds and one kindcorresponding to metal to be a cathode) are evaporated.

Then, after CuPc that is the hole injecting material is evaporated by 10nm to form a hole injecting region 503, the evaporation of α-NPD that isthe hole transporting material is started while CuPc is vaporized,whereby a mixed region 511 composed of CuPc and α-NPD is formed. Themixed region 511 is set to have a thickness of 10 nm.

Next, the evaporation of CuPc is stopped, and only α-NPD is evaporatedby 30 nm to form a hole transporting region 504. Thereafter, evaporationof CBP that is a host material is started while α-NPD is vaporized,whereby a mixed region 512 composed of α-NPD and CBP is formed. Themixed region 512 is set to have a thickness of 10 nm.

Next, the evaporation of α-NPD is stopped, and CBP is evaporated by 20nm to form a light emitting region 505. During the formation of thelight emitting region 505. PtOEP as the triplet light emitting materialfor red color is doped at 4 wt %. Thereafter, the vaporization of PtOEPis finished, and evaporation of BCP which is the blocking material, isstarted while CBP is vaporized, whereby a mixed region 513 composed ofCBP and BCP is formed. The mixed region 513 is set to have a thicknessof 5 nm.

Then, the evaporation of CBP is stopped, and BCP is evaporated by 10 nmto form a blocking region 506. Thereafter, while BCP is vaporized,evaporation of Alq₃ which is the electron transporting material, isstarted whereby a mixed region 514 composed of BCP and Alq₃ is formed.The mixed region 514 is set to have a thickness of 5 nm.

Subsequently, the evaporation of BCP is stopped, and Alq₃ is evaporatedto form an electron transporting region 507 with a thickness of 40 nm.The evaporation of Alq₃ is finished, and at the same time, evaporationof Li(acac), which is the electron injecting material, is startedwithout any interval to evaporate by approximately 2 nm. The reason theinterval is not put is only that the formation of an impurity layer isprevented as described above.

Finally, aluminum as the cathode is evaporated by approximately 150 nm.Thus, a triplet light emitting element for emitting red color whichderives from PtOEP is obtained.

Embodiment 3

In this embodiment, the structure of each pixel of the display deviceshown in FIGS. 9A to 9E, is specifically exemplified. The evaporationdevice shown in FIG. 8 is used as the evaporation device to thereby formeach pixel. Note that the reference numerals in FIG. 8 and FIGS. 9A to9E are referred herein below.

First, the substrate shown in FIG. 9A is carried into the evaporationchamber 801 for red pixel, and a triplet light emitting element for redcolor as shown in FIG. 10A is manufactured. Here, CuPc is the holeinjecting material, α-NPD is the hole transporting material, BAlq₂ isthe electron transporting material, and Alq₃ is the electron injectingmaterial. PtOEP is doped into a mixed region composed of α-NPD andBAlq₂. The weight ratio thereof is set to α-NPD:BAlq₂:PtOEP=20:80:4.Note that attention is paid to in order that intervals are not occurredbetween CuPc and α-NPD and between BAlq₂ and Alq₃ to thereby prevent theformation of an impurity layer.

Next, the substrate is carried into the evaporation chamber 802 forgreen pixel, and a green singlet light emitting element having the mixedregion shown in FIG. 10B is manufactured. Here. CuPc is the holeinjecting material. α-NPD is the hole transporting material, and Alq₃ isthe electron transporting material and also light emitting material. Theweight ratio in the mixed region is set to α-NPD:Alq₃=50:5). Note thatattention is paid to in order that an interval is not occurred betweenCuPc and α-NPD to thereby prevent the formation of an impurity layer.

Further, the substrate is carried into the evaporation chamber 803 forblue pixel, and a blue singlet light emitting element including themixed region shown in FIG. 10C is manufactured. Here, CuPc is the holeinjecting material, α-NPD is the hole transporting material and alsolight emitting material. BAlq₂ is the electron transporting material,and Alq₃ is the electron injecting material. The weight ratio in themixed region is set to α-NPD:BAlq₂=20:80. Note that attention is paid toin order that intervals are not occurred between CuPc and α-NPD andbetween BAlq₂ and Alq₃ to thereby prevent the formation of an impuritylayer.

Finally, an Al:Li alloy is evaporated by approximately 150 nm as acathode. Thus, a full-color display device, in which a pixel for redcolor light emission which derives from PtOEP, a pixel for green colorlight emission which derives from Alq₃ and a pixel for blue color lightemission which derives from α-NPD are used, can be realized.

Embodiment 4

A whole structure of a full-color light emitting device as shown inEmbodiment 3 is described in this Embodiment.

FIG. 11 is a cross sectional diagram of an active matrix light emittingdevice that uses the organic light emitting elements of the presentinvention. Note that although thin film transistors (hereafter referredto as TFTs) are used here as active elements, MOS transistors may alsobe used.

Further, the example shown here uses top gate TFTs (specifically, planerTFTs) as the TFTs, but bottom gate TFTs (typically reverse stagger TFTs)can also be used.

Reference numeral 1101 denotes a substrate in FIG. 11, and a substratethrough which visible light can pass is used as the substrate.Specifically, a glass substrate, a quartz substrate, a crystallizedglass substrate, or a plastic substrate (including plastic films) may beused. Note that an insulating film formed on the surface is alsoincluded in the substrate 1101.

A pixel portion 1111 and a driver circuit portion 1112 are formed on thesubstrate 1101. The pixel portion 1111 is explained first.

The pixel portion 1111 is a region for performing image display. Aplurality of pixels exist on the substrate, and a TFT 1102 forcontrolling the amount of electric current flowing in an organic lightemitting element (hereafter referred to as an electric current controlTFT), a pixel electrode (anode) 1103, an organic compound film 1104, anda cathode 1105 are formed in each pixel. Note that although only theelectric current control TFT is shown in FIG. 11, a TFT for controllingthe amount of voltage applied to a gate of the electric current controlTFT (hereafter referred to as a switching TFT) is also formed.

It is preferable that a p-channel TFT be used for the electric currentcontrol TFT 1102. Although it is possible to use an n-channel TFT, usinga p-channel TFT can more effectively suppress the amount of electriccurrent consumption in the case where an anode of the organic lightemitting element is connected to the electric current control TFT, asshown in FIG. 11.

Further, the pixel electrode 1103 is electrically connected to a drainof the electric current control TFT 1102. A conductive material having awork coefficient of 4.5 to 5.5 eV is used as a material for the pixelelectrode 1103 in Embodiment 4, and therefore the pixel electrode 1103functions as the anode of the organic light emitting element. Indiumoxide, tin oxide, zinc oxide, or a compound of these (such as ITO) maytypically be used as the pixel electrode 1103. The organic compound film1104 is formed on the pixel electrode 1103.

In addition, the cathode 1105 is formed on the organic compound film1104. It is preferable to use a conductive material having a workcoefficient from 2.5 to 3.5 eV as a material for the cathode 1105. Aconductive film containing an alkaline metal element or an alkalineearth metal element, a conductive film containing aluminum, a laminationof these conductive films with aluminum or silver, and the like maytypically be used as the cathode 1105.

Further, the layer composed of the pixel electrode 1103, the organiccompound film 1104, and the cathode 1105 is covered by a protective film1106. The protective film 1106 is formed in order to protect the organiclight emitting elements from oxygen and water. Silicon nitride, siliconoxynitride, aluminum oxide, tantalum oxide, or carbon (typically diamondlike carbon) is used as a material for the protective film 1106.

The driver circuit 1112 is explained next. The driver circuit 1112 is aregion for controlling the timing of signals sent to the pixel portion1111 (gate signals and data signals), and a shift register, a buffer, alatch, an analog switch (transfer gate) and a level shifter are formed.A CMOS circuit composed of an n-channel TFT 1107 and a p-channel TFT1108 is shown in FIG. 11 as a basic unit for these circuits.

Note that known structures may be used for the circuit structures of theshift register, the buffer, the latch, the analog switch (transfergate), and the level shifter circuits. Further, although the pixelportion 1111 and the driver circuit 1112 are formed on the samesubstrate in FIG. 11, an IC or LSI can also be electrically connectedwithout forming the driver circuit.

Furthermore, although the pixel electrode (anode) 1103 is electricallyconnected to the electric current control TFT 1102 in FIG. 11, astructure in which the cathode is connected to the electric currentcontrol TFT can also be used. In this case, the pixel electrode may beformed by the same material as that of the cathode 1105, and the cathodemay be formed by the same material as that of the pixel electrode(anode) 1103. It is preferable that the electric current control TFT bean n-channel TFT in this case.

The light emitting device shown in FIG. 11 is one manufactured by a stepof forming a wiring 1109 after forming the pixel electrode 1103. In thiscase there is the possibility that the pixel electrode 1103 will havesurface roughness. The organic light emitting element is an electriccurrent driven element, and therefore it is thought that its propertieswill deteriorate due to surface roughness of the pixel electrode 1103.

A light emitting device in which a pixel electrode 1203 is formed afterforming a wiring 1209 can also be considered, as shown in FIG. 12. Inthis case, electric current injection from the pixel electrode 1203 isimproved compared to the structure of FIG. 11.

Further, each pixel arranged in the pixel portion 1111 and the pixelportion 1211 is separated by positive taper bank shape structures 1110and 1210 in FIG. 11 and FIG. 12, respectively. The bank shape structurecan also be structured such that the bank shape structure does notcontact the pixel electrode by using a reverse taper structure, forexample. An example thereof is shown in FIG. 13.

A wiring and separation portion 1310, serving both as a wiring and aseparation portion, is formed in FIG. 13. The shape of the wiring andseparation portion 1310 shown in FIG. 13 (a structure having anoverhang) can be formed by laminating a metal which composes a wiring,and a material having an etching rate lower than that of the metal (forexample, a metal nitride), and then performing etching thereto. Shortcircuits between a pixel electrode 1303 or the wiring, and a cathode1305, can be prevented due to such a shape. Note that, differing from anormal active matrix light emitting device, a structure in which thecathodes 1305 on the pixels are given a stripe shape (similar tocathodes in passive matrix light emitting device) is shown in FIG. 13.

An external view of the active matrix light emitting device of FIG. 12is shown in FIG. 14. Note that FIG. 14A shows a top surface diagram, andthat a cross sectional diagram in which FIG. 14A is cut along a line P-Pis shown in FIG. 14B. Further, the symbols used in FIG. 12 are also usedin FIGS. 14A and 14B.

Reference numeral 1401 in FIG. 14A denotes a pixel portion, referencenumeral 1402 denotes a gate signal line driver circuit, and referencenumeral 1403 denotes a data signal line driver circuit. Further, signalssent to the gate signal line driver circuit 1402 and to the data signalline driver circuit 1403 are input from a TAB (tape automated bonding)tape 1405, through an input wiring 1404. Note that, although not shownin the figures, a TCP (tape carrier package) in which an IC (integratedcircuit) is formed in a TAB tape may be connected instead of the TABtape 1405.

Reference numeral 1406 denotes a cover material formed above the organiclight emitting elements shown in FIG. 12, and the cover material 1406 isbonded using a sealant 1407 made from a resin. Any material may be usedfor the cover material 1406, provided that oxygen and water cannot passthrough the material. As shown in FIG. 14B, a cover made from a plasticmaterial 1406 a, and having carbon films 1406 b and 1406 c(specifically, diamond like carbon films) formed on the obverse andreverse surfaces of the plastic material 1406 a, is used in Embodiment4.

In addition, the sealant 1407 is covered by a sealing material 1408 madefrom a resin, and the organic light emitting elements are completelyencapsulated in a closed space 1409 as shown in FIG. 14B. The sealedspace 1409 may then be filled with an inert gas (typically nitrogen gasor a noble gas), a resin, or an inert liquid (for example, a liquidstate fluorocarbon, typically perfluoroalkane). In addition, it is alsoeffective to form a hygroscopic agent or a deoxidant.

Further, a polarization plate may also be formed in a display surface ofthe light emitting device (a surface on which images are observed)according to Embodiment 4. The polarization plate suppresses reflectionof light made incident from the outside, and is effective in preventinga user s own image from being projected into the display surface. Acircular polarization plate is generally used. However, it is preferableto use a structure which gives little internal reflection, by adjustingthe index of refraction, in order to prevent light emitted from theorganic compound layer from being reflected by the polarization plateand returning to the inside.

Note that any of the organic light emitting elements disclosed by thepresent invention may be used as the organic light emitting elementscontained in the light emitting device of Embodiment 4.

Embodiment 5

In this embodiment, a passive matrix light emitting device will bedescribed as an example of a light emitting device including an organicEL device disclosed by the present invention. FIG. 15A is a top viewthereof and FIG. 15B is a cross sectional view obtained by cutting FIG.15A along a dashed line P-P′.

In FIG. 15A, reference numeral 1501 denotes a substrate and a plasticmember is used here. As the plastic member, a plate shaped or a filmshaped member made of polyamide, polyamide, acrylic resin, epoxy resin,PES (polyether sulfone), PC (polycarbonate), PET (polyethyleneterephthalate) or PEN (polyether nitrile) can be used.

Reference numeral 1502 denotes scan lines (anode layers) made fromconductive oxide films. In this embodiment, conductive oxide films inwhich gallium oxide is added to zinc oxide are used. Reference numeral1503 denotes data lines (cathode layers) made from metal films. In thisembodiment, an bismuth films are used. Reference numeral 1504 denotesbanks made of acrylic resins. The banks 1504 function as isolation wallsfor separating the data lines 1503. Both the scan lines 1502 and thedata line 1503 are formed with stripe shapes and provided orthogonal toeach other. Note that although not shown in FIG. 15A, an organiccompound layer is sandwiched between the scan lines 1502 and the datalines 1503 and intersection portions 1505 become pixels.

The scan lines 1502 and the data lines 1503 are connected with anexternal driver circuit through a TAB tape 1507. Note that referencenumeral 1508 denotes a wiring group made from a set of scan lines 1502and reference numeral 1509 denotes a wiring group made from a set ofconnection wirings 1506 connected with the data lines 1503. Also,although not shown, instead of the TAB tape 1507, a TCP in which an ICis provided in the TAB tape may be connected with the scan lines and thedata lines.

In FIG. 15B, reference numeral 1510 denotes a sealing member andreference numeral 1511 denotes a cover member adhered to the plasticsubstrate 1501 through the sealing member 1510. A light curable resin ispreferably used as the sealing member 1510 and a material in whichdegassing is less and which has low hygroscopicity is preferable. It ispreferable that the cover member is made of the same material as thesubstrate 1501 and glass (including quartz glass) or plastic can beused. Here, a plastic member is used.

Next, an enlarged view of a structure of a pixel region 1512 is shown inFIG. 15C. Reference numeral 1513 denotes an organic compound layer. Notethat, as shown in FIG. 15C, banks 1504 are formed with a shape in whicha width of the lower layer is narrower than that of the upper layer, andthus the data lines 1503 can be physically separated form each other. Apixel portion 1514 surrounded by the sealing member 1510 is blocked fromoutside air by a sealing member 1515 made of a resin, and thus astructure is obtained such that deterioration of the organic compoundlayer is prevented.

In the light emitting device of the present invention having the abovestructure, the pixel portion 1514 is constructed by the scan lines 1502,the data lines 1503, the banks 1504, and the organic compound layer1513. Thus, the light emitting device can be manufactured by a verysimple process.

Also, a polarization plate may be provided in a display screen (imageviewing surface) of the light emitting device described in thisembodiment. This polarization plate has an effect that the reflection oflight incident from the outside is suppressed and a viewer is preventedfrom being reflected in the display screen. Generally, a circularpolarization plate is used. Note that, in order to prevent the casewhere light emitted from the organic compound layer is reflected by thepolarization plate and returned to the inner portion, it is preferableto use a structure in which the refractive index is adjusted to reduceinner reflection.

Note that, as the organic EL element included in the light emittingdevice of this embodiment, any one of the organic EL elements disclosedby the present invention may be used.

Embodiment 6

In this embodiment, an example of a module in which a printed wiringboard is provided in the light emitting device described in Embodiment 5will be described.

In a module shown in FIG. 16A, a TAB tape 1604 is attached to asubstrate 1601 (here, including a pixel portion 1602 and wirings 1603 aand 1603 b) and a printed wiring board 1605 is attached to the substrate1601 through the TAB tape 1604.

Here, a functional block view of the printed wiring board 1605 is shownin FIG. 16B. An IC which functions as at least I/O ports (input portionand output portion) 1606 and 1609, a data signal side driver circuit1607, and a gate signal side driver circuit 1608 is provided in theinner portion of the printed wiring board 1605.

Therefore, the module in which the TAB tape is attached to the substratein which the pixel portion is formed on a substrate surface and theprinted wiring board having a function as the driver circuit is attachedto the substrate through the TAB tape is called a driver circuitexternal module in particular in this specification.

Note that, as the organic EL element included in the light emittingdevice of this embodiment, any one of the organic EL elements disclosedby the present invention may be used.

Embodiment 7

In this embodiment, an example of a module in which a printed wiringboard is provided in the light emitting device described in Embodiment 4or 5 will be described.

In a module shown in FIG. 17A, a TAB tape 1705 is attached to asubstrate 1701 (here, including a pixel portion 1702, a data signal sidedriver circuit 1703, a gate signal side driver circuit 1704, and wirings1703 a and 1704 a) and a printed wiring board 1706 is attached to thesubstrate 1701 through the TAB tape 1705. A functional block view of theprinted wiring board 1706 is shown in FIG. 17B.

As shown in FIG. 17B, an IC which functions as at least I/O ports 1707and 1710 and a control portion 1708 is provided in the inner portion ofthe printed wiring board 1706. Note that, although a memory portion 1709is provided here, it is not necessarily provided. Also, the controlportion 1708 has a function of controlling operations of the drivercircuits, correction of image data, and the like.

Therefore, the module in which the printed wiring board having afunction as the controller is attached to the substrate in which theorganic EL element is formed is called a controller external module inparticular in this specification.

Note that, as the organic EL element included in the light emittingdevice of this embodiment, any one of the organic EL elements disclosedby the present invention may be used.

Embodiment 8

An example of a light emitting device in which triplet light emittingelements like those shown by Embodiment 1 and 2 are driven by a digitaltime gray scale display is show n in Embodiment 8. The light emittingdevice of Embodiment 8 is extremely useful because high efficiency lightemission can be achieved by utilizing light emitted from a tripletexcitation state, and at the same time a uniform image can be obtainedby employing digital time gray scale display.

A circuit structure of a pixel used in the organic light emittingelement is shown in FIG. 18A. Reference symbols Tr1 and Tr2 denotetransistors, and reference symbol Cs denotes a storage capacitor. Anelectric current flows from a source line to the transistor Tr1 in thiscircuit if a gate line is selected, and a voltage corresponding to thatsignal is stored in the storage capacitor Cs. An electric currentcontrolled by a voltage Vgs between a gate and a source of thetransistor Tr2 then flows in the transistor Tr2 and in the organic lightemitting element.

The transistor Tr1 is placed in an off state after Tr1 has beenselected, and the voltage Vgs of the storage capacitor Cs is stored. Theelectric current depending only upon the voltage Vgs can thereforecontinue to flow.

A chart for showing driving this type of circuit by digital time grayscale display is shown in FIG. 18B. One frame is divided into aplurality of sub-frames, and 6 bit gray scale is shown in FIG. 18B withone frame divided into 6 sub-frames. The ratio of light emitting periodsfor each of the sub-frames becomes 32::16::8::4::2::1 in this case.

The concept of a driver circuit of the TFT substrate in Embodiment 8 isshown in FIG. 18C. A gate driver and a source driver are formed on thesame substrate. A pixel circuit and a driver are set so as to performdigital drive, and therefore a uniform image can be obtained that is notinfluenced by dispersion in the TFT properties.

Embodiment 9

The light emitting devices of the present invention which have beendescribed in the embodiments above have advantages of low powerconsumption and long lifetime. Accordingly, electric appliances thatinclude those light emitting devices as their display units can operateconsuming less power than conventional ones and are durable. Theadvantages are very useful especially for electric appliances that usebatteries as power sources, such as portable equipment, because lowpower consumption leads directly to conveniences (batteries lastlonger).

The light emitting device is self-luminous to eliminate the need forback light as the one in liquid crystal displays, and has an organiccompound film whose thickness is less than 1 μm. Therefore the lightemitting device can be made thin and light-weight. Electric appliancesthat include the light emitting device as their display units areaccordingly thinner and lighter than conventional ones. This too leadsdirectly to conveniences (lightness and compactness in carrying themaround) and is very useful particularly for portable equipment and likeother electric appliances. Moreover, being thin (unvoluminous) isdoubtlessly useful for all of the electric appliances in terms oftransportation (a large number of appliances can be transported in amass) and installation (space-saving).

Being self-luminous, the light emitting device is characterized byhaving better visibility in bright places than liquid crystal displaydevices and wide viewing angle. Therefore electric appliances thatinclude the light emitting device as their display units areadvantageous also in terms of easiness in viewing display.

To summarize, electric appliances that use a light emitting device ofthe present invention have, in addition to merits of conventionalorganic light emitting elements, namely, thinness/lightness and highvisibility, new features of low power consumption and long lifetime, andtherefore are very useful.

This embodiment shows examples of the electric appliances that includeas display units the light emitting device of the present invention.Specific examples thereof are shown in FIGS. 19 and 20. The organiclight emitting element included in the electric appliance of thisembodiment can be any element according to the present invention. Thelight emitting device included in the electric appliance of thisembodiment can have any of the configurations illustrated in FIGS. 11 to18.

FIG. 19A shows a display device using an organic light emitting element.The display is composed of a case 1901 a, a support base 1902 a, and adisplay unit 1903 a. By using a light emitting device of the presentinvention as the display unit 1903 a, the display can be thin andlight-weight, as well as durable. Accordingly, transportation issimplified, space is saved in installation, and lifetime is long.

FIG. 19B shows a video camera, which is composed of a main body 1901 b,a display unit 1902 b, an audio input unit 1903 b, operation switches1904 b, a battery 1905 b, and an image receiving unit 1906 b. By using alight emitting device of the present invention as the display unit 1902b, the video camera can be thin and light-weight, and consumes lesspower.

Accordingly, battery consumption is reduced and carrying the videocamera is less inconvenient.

FIG. 19C shows a digital camera, which is composed of a main body 1091c, a display unit 1902 c, an eye piece unit 1903 c, and operationswitches 1904 c. By using a light emitting device of the presentinvention as the display unit 1902 c, the digital camera can be thin andlight-weight, and consumes less power. Accordingly, battery consumptionis reduced and carrying the digital camera is less inconvenient.

FIG. 19D shows an image reproducing device equipped with a recordingmedium. The device is composed of a main body 1901 d, a recording medium(such as CD, LD, or DVD) 1902 d, operation switches 1903 d, a displayunit (A) 1904 d, and a display unit (B) 1905 d. The display unit (A)1904 d mainly displays image information whereas the display unit (B)1905 d mainly displays text information. By using a light emittingdevice of the present invention as the display unit (A) 1904 d and thedisplay unit (B) 1905 d, the image reproducing device consumes lesspower and can be thin and light-weight as well as durable. The imagereproducing device equipped with a recording medium also includes CDplayers and game machines.

FIG. 19E shows a (portable) mobile computer, which is composed of a mainbody 1901 e, a display unit 1902 e, an image receiving unit 1903 e, aswitch 1904 e, and a memory slot 1095 e. By using a light emittingdevice of the present invention as the display unit 1902 e, the portablecomputer can be thin and light-weight, and consumes less power.Accordingly, battery consumption is reduced and carrying the computer isless inconvenient. The portable computer can store information in aflash memory or a recording medium obtained by integrating non-volatilememories and can reproduce the stored information.

FIG. 19F shows a personal computer, which is composed of a main body1901 f, a case 1902 f, a display unit 1903 f, and a keyboard 1904 f. Byusing a light emitting device of the present invention as the displayunit 1903 f, the personal computer can be thin and light-weight, andconsumes less power. The light emitting device is a great merit in termsof battery consumption and lightness especially for a notebook personalcomputer or other personal computers that are carried around.

These electric appliances now display with increasing frequencyinformation sent through electronic communication lines such as theInternet and radio communications such as radio wave, especially,animation information. Since organic light emitting elements have veryfast response speed, the light emitting device is suitable for animationdisplay.

FIG. 20A shows a cellular phone, which is composed of a main body 2001a, an audio output unit 2002 a, an audio input unit 2003 a, a displayunit 2004 a, operation switches 2005 a, and an antenna 2006 a. By usinga light emitting device of the present invention as the display unit2004 a, the cellular phone can be thin and light-weight, and consumesless power. Accordingly, battery consumption is reduced, carrying thecellular phone is easy, and the main body is compact.

FIG. 20B shows audio (specifically, car audio), which is composed of amain body 2001 b, a display unit 2002 b, and operation switches 2003 band 2004 b. By using a light emitting device of the present invention asthe display unit 2002 b, the audio can be thin and light-weight, andconsumes less power. Although car audio is taken as an example in thisembodiment, the audio may be home audio.

It is effective to give the electric appliances shown in FIGS. 19 to 20a function of modulating the luminance of emitted light in accordancewith the brightness of the surroundings where the electric appliancesare used by providing the electric appliances with photo sensors asmeasures to detect the brightness of the surroundings. A user canrecognize image or text information without difficulties if the contrastratio of the luminance of emitted light to the brightness of thesurroundings is 100 to 150. With this function, the luminance of animage can be raised for better viewing when the surroundings are brightwhereas the luminance of an image can be lowered to reduce powerconsumption when the surroundings are dark.

The reduction in luminance of the triplet light emitting element for redcolor can be suppressed to lengthen the element life by implementing thepresent invention. Thus, the organic light emitting element for redcolor can be provided in which emission efficiency is high and a life islong in comparison with prior art.

Further, the display device can be provided in which a balance of thethree primary colors of light is favorable, besides, power consumptionis low, and a change of color fluctuation with time is small incomparison with prior art, by using the triplet light emitting elementfor red color and the singlet light emitting elements for green colorand blue color. Furthermore, the electric device can be provided inwhich power consumption is low in comparison with prior art and whichhas a display portion exhibiting a clear display that never fades evenwith the lapse of time by using the above-mentioned display device.

1. (canceled)
 2. A light-emitting device comprising: a firstlight-emitting element over a substrate; and a second light-emittingelement over the substrate, wherein the first light-emitting elementcomprises a mixed region between a pair of electrodes, wherein the firstlight-emitting element comprises a material capable of emitting lightfrom a triplet excitation state, wherein the second light-emittingelement comprises a material capable of emitting light from a singletexcitation state, and wherein the mixed region comprises the materialcapable of emitting light from the triplet excitation state.
 3. Thelight-emitting device according to claim 2, wherein the material capableof emitting light from the singlet excitation state exhibits blue colorlight emission.
 4. The light-emitting device according to claim 2,wherein the first light-emitting element and the second light-emittingelement are not overlapped with each other.
 5. The light-emitting deviceaccording to claim 2, wherein the mixed region comprises a holetransporting material and an electron transporting material.
 6. Anelectronic device having the light-emitting device according to claim 2,wherein the electronic device is one selected from the group consistingof a video camera, digital camera, mobile computer, personal computer,and cellular phone.
 7. The light-emitting device according to claim 2,wherein the substrate comprises a plastic member.
 8. The light-emittingdevice according to claim 7, wherein the plastic member comprises atleast one selected from the group consisting of polyimide, polyamide,acrylic resin, epoxy resin, polyether sulfone, polycarbonate,polyethylene terephthalate and polyether nitrile.
 9. A light-emittingdevice comprising: a first light-emitting element over a substrate; anda second light-emitting element over the substrate, wherein the firstlight-emitting element comprises a mixed region between a pair ofelectrodes, wherein the first light-emitting element comprises amaterial capable of emitting light from a triplet excitation state,wherein the second light-emitting element comprises a material capableof emitting light from a singlet excitation state, wherein the materialcapable of emitting light from the triplet excitation state includes aniridium complex exhibiting red color light emission, and wherein themixed region comprises the material capable of emitting light from thetriplet excitation state.
 10. The light-emitting device according toclaim 9, wherein the material capable of emitting light from the singletexcitation state exhibits blue color light emission.
 11. Thelight-emitting device according to claim 9, wherein the firstlight-emitting element and the second light-emitting element are notoverlapped with each other.
 12. The light-emitting device according toclaim 9, wherein the mixed region comprises a hole transporting materialand an electron transporting material.
 13. An electronic device havingthe light-emitting device according to claim 9, wherein the electronicdevice is one selected from the group consisting of a video camera,digital camera, mobile computer, personal computer, and cellular phone.14. The light-emitting device according to claim 9, wherein thesubstrate comprises a plastic member.
 15. The light-emitting deviceaccording to claim 14, wherein the plastic member comprises at least oneselected from the group consisting of polyimide, polyamide, acrylicresin, epoxy resin, polyether sulfone, polycarbonate, polyethyleneterephthalate and polyether nitrile.
 16. A light-emitting devicecomprising: a first transistor over a substrate; a second transistorover the substrate; a first light-emitting element over the firsttransistor; and a second light-emitting element over the secondtransistor, wherein the first light-emitting element comprises a mixedregion between a pair of electrodes, wherein the first light-emittingelement comprises a material capable of emitting light from a tripletexcitation state, wherein the second light-emitting element comprises amaterial capable of emitting light from a singlet excitation state, andwherein the mixed region comprises the material capable of emittinglight from the triplet excitation state.
 17. The light-emitting deviceaccording to claim 16, wherein the material capable of emitting lightfrom the singlet excitation state exhibits blue color light emission.18. The light-emitting device according to claim 16, wherein the firstlight-emitting element and the second light-emitting element are notoverlapped with each other.
 19. The light-emitting device according toclaim 16, wherein the mixed region comprises a hole transportingmaterial and an electron transporting material.
 20. An electronic devicehaving the light-emitting device according to claim 16, wherein theelectronic device is one selected from the group consisting of a videocamera, digital camera, mobile computer, personal computer, and cellularphone.
 21. The light-emitting device according to claim 16, wherein thesubstrate comprises a plastic member.
 22. The light-emitting deviceaccording to claim 21, wherein the plastic member comprises at least oneselected from the group consisting of polyimide, polyamide, acrylicresin, epoxy resin, polyether sulfone, polycarbonate, polyethyleneterephthalate and polyether nitrile.